The invention relates to a cored wire for introducing additives into a molten metal bath.
Steels, irons, etc., are materials whose mechanical or other properties particularly depend on the complex composition of the material.
In order to obtain a material having certain properties from a basic composition, the content of certain elements is adjusted to obtain the desired composition.
It has been known for about twenty years to adjust the composition of molten material by introducing a cored wire of predetermined length into it.
This cored wire is constituted by a metallic casing containing the additive that one wishes to introduce into the molten bath.
The quantity of additive per meter being known, it is relatively simple to adjust the composition of the bath.
In the first cored wires produced, the metallic casing was simply folded so as to place the two edges of the formed strip side by side.
An inner sheet was first put in place in order to close the gap that remained between the edges of said strip, but this was not very effective given that this cored wire was subjected to a winding operation on a reel, then an unwinding operation during its utilization.
This solution was quickly replaced by a different closure for the strip.
This method consists of mechanically crimping the two edges of the strip.
More precisely, it consists of rolling the two edges together so that the edges are fastened to one another. This prevents losses of the additive contained in said strip.
This solution, which makes it possible to adjust a composition by introducing a cored wire into the molten material, works very well with most additives.
However, problems arise with certain additives such as calcium, magnesium, selenium, sulfur and others.
In essence, for some of these additives, the heat of the molten metal bath causes the cored wire to explode in an area very close to the surface of the bath.
Other additives vaporize very quickly and close to the surface. This produces a strong surface reactivity, which results in an oxidation and/or renitriding of the bath, splashes of the liquid metal that damage the material, and heavy smoke emanation. Therefore, this introduction operation is much less efficient in the presence of these additives, and the resulting safety conditions are not adapted for industrial utilization.
In an attempt to eliminate this problem, it is known to introduce the cored wire through a tube made of refractory material immersed in the bath. The use of this tube is very difficult and very costly.
It is known to cover this metallic sheath with a wrapping which, being combustible without leaving any harmful residues, momentarily retards the propagation of heat to the core of the cored wire. This combustible wrapping is wound in a helix around the metallic sheath. Unfortunately, the paper wrapping is sometimes observed to deteriorate during handling, i.e., when the wire is wound around the reel or when the wire placed on the reel is unwound in order to be introduced into the bath.
The subject of the invention is a cored wire comprising a metallic sheath containing an additive and covered by a wrapping 7 which, being combustible without leaving any harmful residues, momentarily retards the propagation of heat to the core of the cored wire.